1. Field of the Invention
This invention relates to a tubbing ring, which is to be used in a tunnel lining and has end faces lying in respective planes. The tubbing comprises an even number of tubbing blocks which have abutting longitudinal side faces so inclined to a line parallel to the longitudinal axis of the ring that the tubbing blocks constitute substantially trapezoidal ring segments, the tubbing blocks being joined by tongue-groove joints at their longitudinal side faces and adjacent rings being adapted to be coupled by coupling means.
2. Description of the Prior Art
Tubbing rings having that basic structure are known from U.S. Pat. No. 4,305,683, which also discloses various joints between adjacent tubbing rings.
Owing to the special shape of the tubbing blocks, the blocks of a tubbing ring can be assembled without requires substantial additional space in the direction in which the tunnel is driven. Owing to the trapezoidal basic shape of said blocks a keystone block which is to be arranged, e.g., at the top requires to be advanced in the direction in which the tunnel is driven beyond the existing portion of the ring only to such an extent that the keystone block can be inserted between the previously placed tubbing blocks which will laterally adjoin the keystone block. The extent to which the keystone block must protrude when it is to be inserted amounts only to a small fractional part of the longitudinal extent of the ring. If the end faces of the tubbing ring do not extend in parallel planes but extend in planes which include an acute angle with each other so that the entire ring in a top view has the configuration of a trapezoid having parallel sides which are constituted by the parallel end faces of the ring, it will be possible for the entire tunnel lining to follow curvatures of the longitudinal axis of the tunnel along a broken line which follows the route or gradient of the tunnel whereas straight sections of the lining can be formed from pairs of rings which have been inverted through 180.degree. about their vertical axes.
In the previous practice the tubbing blocks are formed with recesses in that surface which constitutes the inside surface of the cylindrical ring and the tubbing blocks were coupled by means of tie bolts inserted into fixing holes in the lateral surfaces defining said recesses. For that purpose those blocks which are to be joined or blocks which are to be attached to an existing ring must provisionally be aligned before the tie bolts are inserted. That aligning is a complicated operation, which can be performed only by skilled workers and owing to the bulkiness of the parts often cannot be performed with the required precision. Whereas it has been proposed to form the concrete block on its longitudinal side faces with grooves and tongues, this will decrease the impact strength of the block and difficulties will arise particularly when a tubbing block is to be inserted between two existing blocks of the same ring, e.g., as the keystone block, because concrete surfaces will virtually not slide on each other and a displacement will result in a substantial abrasion. For this reason the tongue-and-groove joints cannot be designed for a close fit but an adequate clearance must be left. The formation of the abutting side faces with a profile has also the disadvantage that the blocks cannot be arranged as pairs of blocks which are inverted relative to each other. Any joint at which the tubbing blocks do not abut in the specified orientation will adversely affect the overall strength of the tubbing ring and will constitute a leak through which water can enter from the rock. It is often impossible to seal such leaks or they can be sealed only by a highly complicated operation.